During the use of a denture for a long period of time, the fitness becomes bad due to absorption of the alveolar ridge and the like, leading to reduction in its retention and stability. Furthermore, when an unfit denture is used, since a non-uniform stress is applied to a mucosa below the denture base, an ulcur and inflammation are likely generated, and a pain may be caused by the occlusal stress. For these reasons, it is necessary to prepare a new denture, or to rebase a denture in use to recover the fitness to the denture mucosa.
However, since the oral mucosa of a patient is in the unstable state for the reasons as described above, it is impossible to recover a good fitness unless these treatments are carried out after the oral mucosa has recovered a healthy state. The material to be used in such a case is a tissue conditioner. The tissue conditioner is laminated on the mucosal surface of a denture in use and used during a period of time of preparing a new denture or rebasing the denture in use.
Since this material is comprised of a powder and a liquid and when mixed, becomes a soft elastic material, if it is lined on the mucosal surface of a denture which has become unfit, the fitness of the denture is recovered so that the pain by the occlusal stress can be mitigated. If the pain is mitigated, the ulcur and inflammation in the oral mucosa disappear, leading to the change of the state of the oral mucosa with a lapse of time. For this reason, the tissue conditioner is provided with such properties that it deforms as the state of the oral mucosa changes. If such properties are not provided, the fitness of the denture is again lost so that the occlusal stress can not be uniformly borne by the entire mucosal surface. For this reason, the tissue conditioner is designed such that it readily generates creeps thereby automatically retain the fitness of the denture. As a material which can meet these requirements, a plastic material comprising a power component consisting of polyethyl methacrylate or a copolymer thereof and a liquid component cconsisting of a phthalic ester-based plasticizer containing about 8 to 20% by weight of ethanol has hitherto been used (see Norio HOSOI, THE JOURNAL OF THE JAPAN DENTAL ASSOCIATION, "Tissue conditioning of complete Denture Patients", Vol. 42, pp. 831-836, 1989).
As described above, these materials must have properties so as to readily generate creeps. For this reason, these materials likely become a material whose physical properties are extremely unstable and when mixed, become tacky so that they are difficult in handling. In addition, they involve the following defects during the use for one to two weeks.
(1) The elasticity is lost. PA1 (2) Displeasing taste and stimulation when applied into the oral cavity. PA1 (3) It is difficult to peel apart from the denture at the time when the tissue conditioner is exchanged. PA1 (a) an ethyl methacrylate polymer powder containing from 1 to 5% by weight of a phthalic ester-based plasticizer; PA1 (b) a copolymer powder represented by the following formula: ##STR3## wherein n/(m+n) is from 0.15 to 0.55, and containing from 0.5 to 2% by weight of a phthalic ester-based plasticizer; and PA1 (c) a mixed powder comprising a polyethyl methacrylate powder having a copolymer powder 30.about.75% by weight represented by the following formula mixed therewith: ##STR4## wherein n/(m+n) is from 0.45 to 0.76. PA1 (1) in the case of the polymer powder (a), the proportion of the phthalic ester-based plasticizer must be from 1 to 5% by weight. PA1 (2) In the case of the copolymer powder (b), the proportion of the phthalic ester-based plasticizer must be from 0.5 to 2% by weight, and the proportion of the isobutyl methacrylate must meet the following relation: ##STR5## wherein n/(n+m) is from 0.15 to 0.55. (3) In the case of the copolymer (c), the proportion of the isobutyl methacrylate must meet the following relation: ##STR6## wherein n/(m+m) is from 0.45 to 0.76.
These defects are considered to be caused by the matter that ethanol contained in the liquid component eluting in the oral cavity. however, if ethanol is excluded from the liquid component, the gelation time of the material greatly increases so that it can not be put into practical use.